1. Field of the Disclosure
The present subject matter is generally directed to particle analysis, and in particular, to systems and methods that may be used for determining the specific gravity and mineralogical properties of solids particles.
2. Description of the Related Art
Many different industries rely on an accurate assessment of the physical properties of particles in order to provide particulate materials, such as powders, suspensions, emulsions, and the like, that can meet a variety of different quality and/or performance characteristics. For example, particle size and shape can greatly influence the flow and/or compaction properties of powders, where larger, more spherically shaped particles will flow more easily than smaller and/or irregularly shaped particles having significant aspect ratios. Furthermore, smaller particles often lead to higher suspension viscosities and an improvement in suspension and/or emulsion stability. Accordingly, significant efforts are employed to determine the shape and measure the size of the particles that are used in and/or created during various processing operations by utilizing a variety of different laboratory techniques.
Following is a brief description of some representative types of prior art devices and techniques that are commonly used to determine particle shape and/or size. It should be appreciated that this is not an exhaustive review of all prior art methods that may be employed or devices that may be used to perform particle size analysis, but is instead intended to simply provide some exemplary general background information on some aspects of the state of the art.
One of the simplest ways of determining the distribution of particle sizes that make up a given particulate material is by sieving, which typically utilizes a woven screen or mesh to separate the various particles by their respective sizes. In general, sieving involves introducing a particulate material sample to the surface of a screen, such as the screen 101 that is shown in top, or plan view, in FIG. 1A. The screen 101 is generally made up of a plurality of crisscrossing wires 102, the size (i.e., diameter or width) and spacing of which define an aperture 103, or open space, between the crisscrossing wires 102. The number of wires over a given linear distance (such as inches) define what is often referred to as a mesh size, or sieve number. During a sieving operation, the screen 101 is shaken or vibrated so that particles which have a size that is smaller than the aperture 103 pass through the screen 101, whereas larger particles remain trapped above the screen 101 by the crisscrossing wires 102.
In many sieving operations, a plurality of stacked screens may be used to separate multiple different particle sizes. For example, FIG. 1B is a partial cutaway top, or plan view, of a screen stack 111 that includes screens 101a/b/c, and FIG. 1C is a side, or elevation view, of the stack 111 shown in FIG. 1B. In a typical multiple screen sieving operation, each of the screens 101a/b/c of the screen stack 111 will have a smaller sized respective aperture 103a/b/c (e.g., a higher mesh number) than the screen immediately thereabove. Therefore, as the particulate matter travels sequentially from the top of the stack 111—where the screen 101a with the largest aperture size 103a is positioned—to the bottom of the stack 111—where the screen 101c with the smallest aperture size 103c is positioned—progressively smaller particles will be trapped on each screen, while only the finest particles pass through the lowermost (highest mesh number) screen 103c. Of course, it should be appreciated the number of screens shown in FIGS. 1B and 1C is illustrative only, as more or fewer screens may be used in the screen stack 111, depending on the targeted basis for the sieving operation. Data that is based on the amount, e.g., weight percent, of each of the different sized particles making up the particulate material sample in question can then be gathered and assessed in order to determine whether the sample meets the requisite quality and or performance standards.
Sieving has some inherent shortcomings that can be problematic when different types of particles and/or materials are mixed together in the same particulate material sample. More specifically, in mixed samples, it is quite often the case that the particles which are able to fit through the aperture of a given screen do not necessarily have the same overall size and shape. For example, particles which have an approximately spherical shape of a given diameter would pass through the same sized screen aperture as an elongated or rod-shaped particle which may have maximum projected sizes/widths in two dimensions that are substantially the same as (or smaller than) that of the spherically shaped particle, but may also have a size/length in the third dimension that is substantially greater than that of the spherically shaped particle. In certain cases, when the screens are vibrated or shaken, particles will have a certain probability of aligning themselves in such a manner as to allow the minimum particle dimensions, such as width or diameter, to pass through the aperture in the screen. Accordingly, particles having completely different shapes and/or volumes may end up together in the same “separated” portion of a sample, simply because they have at least two dimensions in common. In such cases, the particle shape—not its minimum nor maximum dimension (or size)—may become a driving factor in proper particle separation.
Another method of determining particle size that has also been in common use for many years is a laser diffraction technique. FIG. 2 schematically depicts an illustrative prior art laser diffraction particle size analyzing apparatus 200 that may be utilized for this purpose. Generally, when using the laser diffraction technique, the size distribution of a plurality of particles 210 can be calculated by measuring a space intensity distribution of the diffracted/scattered light 204 that is generated when the particles 210 are irradiated with one or more laser beams 201 (one shown in FIG. 2) from one or more laser light sources 202 (one shown in FIG. 2) while the particles 210 are in a substantially dispersed or separated state. Thereafter, data from the diffracted/scattered light 204 may be used to calculate particle sizes based on light scattering and diffraction theories that are well known in the art.
During operation of the illustrative laser diffraction apparatus 200 shown in FIG. 2, a particulate material sample 231 containing the particles 210 is directed from a sample source 230 to a sample cell 206 so that data on the particles 210 can be obtained. Light 205 from a laser light source 202 is used to irradiate the group of particles 210 by passing the light 205 through a collimating lens 203, which is used to focus the light 205 into a parallel laser beam 201. The laser beam 201 is then diffracted or scattered by the particles 210 as they pass through the sample cell 206 so as to thereby form a spatial light intensity distribution pattern. The forward diffracted/scattered light 204 is converged by a lens 207 to form ring-shape diffracted/scattered images on a detection plane 220 disposed at a focal distance position. The intensity distribution pattern of the forward diffracted/scattered light 204 is detected by a ring detector (forward diffracted/scattered light sensor) 208 formed from a plurality of light sensor elements 208e having ring-shape light receiving surfaces of different radii that are arranged concentrically on the detection plane 220. The sideward diffracted/scattered light 204 is detected by sideward diffracted/scattered light sensors 209s and the backward diffracted/scattered light 204 is detected by backward diffracted/scattered light sensors 209b. Thereafter, the space intensity distribution pattern of the diffracted/scattered light 204 that is measured by each of the various plurality of light sensors 208e, 209s, 209b is digitized by an analog/digital converter apparatus (not shown) and input to data processing apparatus 250, such as a computer with suitable analysis software and the like, as the diffracted/scattered light intensity distribution data. Particle size and particle size distribution information can then be calculated with the data processing apparatus 250 as previously noted, i.e., based upon the diffracted/scattered light intensity distribution data, from which quality and performance assessments of the particulate material sample can then be made.
As with sieving, the laser diffraction measurement technique may also present some problems associated with particle shape. This is because laser diffraction does not directly evaluate a given particle size, but instead gathers information from the diffracted/scattered light intensity which is then used to indirectly calculate particle volumes. The algorithms that are typically used to calculate particle size based upon the diffracted/scattered light intensity distribution data thus provide information on particle size that is based on a theoretical equivalent spherical diameter, as the gathered data provides little, if any, information on shape. Therefore, when analyzing a particulate material sample containing a mixture of different types of particles made up of different materials and/or having substantially different shapes, the laser diffraction technique may not be able to distinguish between such varied particles.
Another technique for measuring particle size and size distribution that has been more recently developed is a digital optical imaging technique. FIG. 3 schematically illustrates an exemplary prior art digital optical imaging apparatus 300 that may be used for this purpose. Generally, when using the digital optical imaging technique, the size distribution of a plurality of particles 310 can be determined by obtaining a plurality of digital images of the particles 310 as they pass in front of a digital camera 302. In some aspects, the digital optical imaging technique is similar to the laser diffraction technique described above in that a particulate material sample 331 containing the particles 310 is typically directed from a sample source 330 to a sample cell 306 where they pass in front of the digital camera 302. As with the laser diffraction apparatus described above, the particles 310 are also generally in a substantially dispersed or separated state as so to avoid undue imaging interference between adjacent or nearby particles.
An optical magnification device 303, such as a lens system and the like, is typically used to magnify and focus the digital camera 302 on the particles 310 as they pass through the sample cell 306. In a typical digital optical imaging apparatus, the front-to-back width 306w of the sample cell is usually narrow, as the depth-of-focus of the digital camera 302 is often limited, particularly when the optical magnification system 303 is operated under very high magnifications for viewing and imaging particles smaller than 200-300 μm (microns). As such, the width 306w is often minimized so that most, if not all, of the particles 310 pass through the focal plane of the digital camera 302 and optical magnification device 303.
In some digital optical imaging systems, such as the apparatus 300 shown in FIG. 3, a light source 301 is positioned so the particles 310 to be measured and the sample cell 306 through which they pass are between the digital camera 302 and the light source 301. During operation of the apparatus 300, the light source 301 is operated so that a light beam 301b from the light source 301 passes through the sample cell 306 and illuminates the particles 310 so that digital images can be captured by the digital camera 302. In many applications, the light source 301 is, for example, a strobe light, such as an LED strobe light and the like, which can be operated to flash up to several thousand times per second, thereby making it is possible to capture a large number of digital images of a single particle while that particle remains in the field of view 302v of the digital camera 302. The various digital images obtained by the digital camera 302 may then be transmitted to an image processing system 350, such as a computer that uses a data analysis program, and the like, and the processed image data may then be used to calculate particle size and size distribution information on the particulate material sample.
In many applications, digital optical imaging systems are generally operated so as to obtain a 2-dimensional or “outline” image of particles. The size of particles in the third dimension are then assumed based upon typical particle configurations for the known types of particles that are being imaged. However, as noted above, when the light source 301 that is used during the imaging process is a high frequency strobe lighting apparatuses, some systems can be operated to obtain numerous images of the same particle while that particle remains within the field of view 302v of the digital camera 302, as described above. With this capability in mind, some digital optical imaging systems have been adapted to impart a spin, or rotational motion, to the particles 310 prior to passing them through the field of view 302v. Digital optical imaging apparatuses that are modified in this way are therefore able to gather more than just routine 2-dimensional image data of a given single particle. Instead, by obtaining numerous sequential 2-dimensional images of the same individual particle as it spins and passes through the field of view 302v, a properly designed data analysis program may enable the image processing system 350 to construct a 3-dimensional image of the particle. In this way, some digital optical imaging systems may theoretically be able to provide more accurate data as to the actual shape of a given particle.
Each of the particle size analysis systems described above may be configured so as to operate as a “dry” system or as a “wet” system. “Dry” systems are those in which the particles to be measured flow through a substantially gaseous medium, such as air or an inert gas and the like. On the other hand, “wet” systems are those wherein the particles flow through and/or with a liquid, such as water, oil, alcohol, and/or mixtures of water or alcohol with other liquids. Liquids are often used as the flow medium when using the laser diffraction or digital optical imaging techniques, as the higher viscosity liquids enable the particles to be diluted and properly dispersed so that accurate measurements and data gathering can be performed.
The various methods and apparatuses described above are generally used to obtain size and shape information about the particles that make up a particulate material sample. While, as previously noted, such information on the size and shape of particles can be helpful in many different applications, there is sometimes a need to obtain information regarding other physical and/or chemical properties of particles that may be beneficial in supporting and even improving certain industrial, manufacturing, or mining operations. The following disclosure is directed to new and unique methods and techniques of utilizing one or more of the particle size analysis apparatuses described above so as to obtain information about the properties of particles other than size and shape, and the systems in which such methods and techniques are implemented.